Packet switching communication networks are commonly employed to transfer digital information over long distances. One type of packet switching communication network is an asynchronous transfer mode communication network. An asynchronous transfer mode communication network enables the transfer of digital voice information, digital video information and digital data over short or long distances via common carrier communication links. Such a communication network enables a wide variety of communication devices to share common carrier communication links on a demand driven basis. For example, such asynchronous transfer mode communication networks are commonly employed for a wide area network (WAN) communication.
The common carrier communication links employed in such asynchronous transfer mode communication networks typically include relatively low speed metal wire based communication links. One such type of relatively low speed common carrier communication link available in North America is the T1 communication link. A typical T1 communication link provides a maximum data rate of 1.544 megabits per second. Similarly, the E1 common carrier communication links available in Europe provide a data rate of 2.048 megabits per second.
In addition, the common carrier communication links employed in such asynchronous transfer mode communication networks usually include higher speed communication links. An example of such a high-speed common carrier communication link available in North America is the T3 communication link, which provides a maximum data rate of 45 megabits per second. An example of a high-speed common carrier communication link available in Europe is the E3 communication link, which provides a maximum data rate of 34 megabits per second.
Prior asynchronous transfer mode communication networks that require high bandwidth communication links typically employ T3 or E3 communication links rather than the lower speed T1 or E1 communication links. Unfortunately, the subscription rates for such T3 common carrier communication links are usually much higher than the subscription rates for T1 or E1 links. Moreover, in North America such T3 common carrier communication links are not as widely available as T1 common carrier communication links. Worse yet, in Europe E3 common carrier communication links are rarely available and E1 common carrier communication links have only recently become widely available.
As a consequence, communication services requiring such high bandwidth communication links typically require a high premium payment for such high speed common carrier communication links. Moreover, such required high-speed communication links may not be available in some areas for such an asynchronous transfer mode communication network.
In addition, some prior asynchronous transfer mode communication networks require communication links with a bandwidth higher than is provided by low speed common carrier communication links such as T1 or E1 but do not require the high bandwidth of the T3 or E3 common carrier communication links. Unfortunately, communication services requiring such medium level bandwidth communication links must typically employ expensive high-speed common carrier communication links even though the full bandwidth range is not needed. For example, an asynchronous transfer mode communication network requiring a maximum data rate of 10 or 20 megabits per second must usually employ high speed T3 or E3 common carrier communication links. Such high-speed common carrier links unnecessarily increase the cost of communication for subscribers to such an asynchronous transfer mode communication networks.
In an Inverse Multiplexing for ATM (IMA) system, ATM cell traffic is transported by means of time-division multiplexing over several channels (typically T1 or E1 data links). In a cell based IMA system, these ATM cells are sent on each channel in a round-robin fashion as depicted in FIGS. 1A–1C.
The receiving IMA device must reconstruct its output stream from cells received over the constituent channels, in such a way that cell sequence integrity is preserved.
Referring to the figures, the basic function of IMA device is to work in pairs to take an ATM cell stream coming from the ATM layer, send it over the multiple links by spreading cells over the available links and ensure that the initial cell stream can be retrieved at the far end. Thus the IMA preferably makes the ATM traffic transparent to the ATM layer over multiple links in use. As far as the ATM layer is concerned, it should only see a pipe (can be considered as a virtual link) whose rate is now the sum of the multiple link rates. It is assumed that each link is run in clear-mode without the presence of intermediate ATM nodes processing ATM cells. This means that there should be no cell discard by any intermediate transmission equipment.